Silicon carbide (SiC) has many excellent properties. For example, compared to silicon (Si), the dielectric breakdown field is larger by one order of magnitude, the band gap is three times larger, and the thermal conductivity is about three times higher. Silicon carbide (SiC) is expected to be applied to power devices, high frequency devices, high temperature operation devices, and the like.
For promoting the practical application of SiC devices, it is essential to establish high-quality SiC epitaxial wafers and high-quality epitaxial growth techniques.
SiC devices are fabricated using SiC epitaxial wafers. The SiC epitaxial wafers are obtained by growing an epitaxial layer (film) to serve as an active region of the device through a chemical vapor deposition (CVD) method or the like on a SiC single crystal substrate obtained by processing from a SiC bulk single crystal grown by a sublimation recrystallization method or the like.
For example, a 4H epitaxial layer is grown by the step-flow growth of SiC (lateral growth from an atomic step) on a SiC single crystal substrate whose growth plane is a plane having an off angle in the <11-20> direction from the (0001) plane.
Among defects contained in the SiC epitaxial wafers, there are defects called carrot defects (carrot type defects, carrot shaped defects) having characteristic shapes exposed on the surface of the epitaxial layer. The carrot defects are representative of defects appearing on the surface of the epitaxial layer, as well as triangular defects, comet defects, and the like. It is desired to reduce the carrot defects in producing the epitaxial wafer for semiconductor devices for which crystal integrity is required since the carrot defects are numerous in numbers and also as large as several tens of micrometers in shape (Patent Documents 1 to 3).
It has been elucidated that the structure of the carrot defect is constituted by a basal plane stacking fault and a prismatic stacking fault and is defined as a distinguishable defect in the field of SiC epitaxial growth. The carrot defects are thought to be formed such that threading dislocations and the like included in the substrate are converted at the time of epitaxial growth.
Several methods have been proposed as a method for reducing the carrot defect density. Patent Document 1 describes a method in which a first epitaxial layer is grown, and then the growth is stopped and the surface is etched, followed by the growth of a second epitaxial layer. Patent Document 2 describes a method of providing a suppression layer of a source gas composition having a low C/Si ratio. Patent Document 3 describes a method of using a substrate in which a pit due to a specific screw dislocation is formed into a certain shape by CMP processing.